Known in the art is a rock drill with independent rotation of a drill bit comprising: an impact unit having a housing with an inner cylindrical cavity accommodating air distributing means and a hammer piston reciprocating under the action of compressed air fed into work-stroke and idle-stroke chambers of the impact unit from said air distributing means, with said hammer piston imparting blows onto the shank of the drill bit at the end of the work stroke thereof; a tool holder provided with a central opening to accommodate said shank, said tool holder being mounted on the front head of the hammer drill and adapted to prevent the drill bit from falling out of the front head; rotary drive means disposed between the impact unit and the front heat comprising a cylinder body disposed normal to the axis of the hammer drill, a piston with a slot in the intermediate portion thereof being accommodated in the inner cavity of said cylindrical body, said piston reciprocating under the action of the compressed air admitted alternatively from the work-stroke chamber and the idle-stroke chamber of the impact unit into the idle and work chambers of said rotary drive means respectively, thereby bringing into motion a lever inserted into the slot of the piston, with said lever being formed integrally with a ratchet wheel engaging pawls mounted in the tool holder which transmits its rotation to the shank of the drill bit.
Thus, the above-disclosed rotary drive means for a rock drill is provided with a ratchet mechanism converting the pivotal movement of the lever imparted thereto from the piston into a rotational movement which is transmitted to the shank of the drill bit by means of the tool holder.
The above-described technical solution complicates the structure of the rotary drive means and makes it unreliable in operation.
Furthermore, a lack of reversing rotations of a drill bit makes it impossible to mechanize the dismounting of a drill string in deep drilling operations.
There is also known in the art a rock drill with independent rotation of a drill bit comprising: two impact units, each being provided with a housing having an inner cylindrcal cavity accommodating a hammer piston reciprocating under the action of compressed air and imparting at the end of its work stroke, blows to one of drill bit shoulders; a front head with the shank of the drill bit being journalled in bearings in said front head and abutting via its shoulder, a spring-loaded flange disposed in the inner cavity of said front head; a tool holder having a central opening to accommodate said shank and adapted to prevent said shank from falling out of the front head; rotary drive means comprising a rotary pneumatic motor having a stationary stator and a rotor journalled in bearings and provided with vanes moved outwardly under the action of centrifugal forces, with said vanes defining work and idle chambers and rotating along with the rotor under the action of compressed air; and a planetary gear with a system of toothed gears reducing the rotational speed of the rotor up to an optimal value and transmitting rotation to the shank of the drill bit (cf. a double-piston hammer drill produced by the firm "Hausgerr").
The provision in this rock drill of a double-piston impact until, a rotary motor, a planetary gear, some pairs of ball bearings and sliding bearings makes it difficult to manufacture, increases its weight and reduces the efficiency of the machine, while a lack of reversing rotation of a drill string makes it impossible to mechanize the dismounting of the drill string in deep drilling operations.